Semiconductor device and manufacturing method thereof

ABSTRACT

The present invention provides a semiconductor device in which a bottom-gate TFT or an inverted stagger TFT arranged in each circuit is suitably constructed in conformity with the functionality of the respective circuits, thereby attaining an improvement in the operating efficiency and reliability of the semiconductor device. In the structure, LDD regions in a pixel TFT are arranged so as not to overlap with a channel protection insulating film and to overlap with a gate electrode by at least a portion thereof. LDD regions in an N-channel TFT of a drive circuit is arranged so as not to overlap with a channel protection insulating film and to overlap with a gate electrode by at least a portion thereof. LDD regions in a P-channel TFT of the drive circuit is arranged so as to overlap with a channel protection insulating film and to overlap with the gate electrode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a manufacturing method of asemiconductor device having a circuit in which a thin film transistor(hereinafter referred to as TFT) is formed on a substrate having aninsulating surface. More particularly, the present invention is suitablefor use in an electro-optical device typically known as a liquid crystaldisplay device having a pixel TFT formed in a display region and a drivecircuit formed in the periphery of the display region on the samesubstrate, and in an electronic equipment mounted with anelectro-optical device with this type. Note that throughout thespecification of the present invention, the semiconductor deviceindicates any device utilizing the semiconductor characteristics forfunctioning, and includes the foregoing electro-optical device and anelectronic equipment mounted with the electro-optical device in itscategory.

2. Description of the Related Art

From the fact that a TFT having an active layer formed of a crystallinesilicon film on a substrate having an insulating surface (hereinafterreferred as a crystalline silicon TFT) has a high electric field effectmobility, it is possible to form a variety of functional circuits. Theabove electro-optical device having such functional circuits integrallyformed on the same substrate has been developed. As a typical example,the active matrix liquid crystal display device is well known.

In the active matrix liquid crystal device employing the crystallinesilicon TFT, a pixel TFT is formed in every pixel of an image displayregion and a drive circuit is formed in the periphery of the imagedisplay region. The drive circuit is composed of a shift resistercircuit, a level shifter circuit, a buffer circuit, a sampling circuit,and the like in which a CMOS circuit as a basic circuit is formed. Thesecircuits are formed on the same substrate, and formed into a unity tocomplete a display device.

The operating conditions of the pixel TFT and the drive circuit are notnecessarily the same. From this, the characteristics that are demandedfor a TFT is somewhat different. For example, the pixel TFT is demandedto function as a switch device for applying a voltage to a liquidcrystal. The liquid crystal is driven by an a.c., thus a method calledframe inverse drive is widely adopted. In this method, for the purposeof maintaining an electric charge of a storage capacitor, thecharacteristic that is demanded for the pixel TFT was to sufficientlylower an off-current value (a drain current that flows during anoff-operation of TFT). On the other hand, since a high drive voltage isapplied to the buffer circuit of the drive circuit, it was necessary toraise the voltage-resistance of the TFT so that it will not break when ahigh voltage is applied. Also, in order to make a current drive abilityhigher, it was necessary to sufficiently secure an on-current value (adrain current that flows during an on-operation of TFT.

However, the point at issue is that the off-current value of thecrystalline silicon TFT easily rises. Moreover, similar to an MOStransistor used in an IC and the like, a deterioration phenomenon suchas a drop of the on-current value is observed on the crystalline siliconTFT. This mainly results from a hot carrier implantation. It has beenconsidered that the hot carrier generated by a high electric field inthe vicinity of the drain triggers the deterioration phenomenon.

As a structure of the TFT to reduce the off-current value, an LDD region(Lightly. Doped Drain) is known. In this structure, there is provided aregion that is added with an impurity element at a low concentrationbetween a channel forming region and a source region or a drain regionwhich is formed by adding an impurity element at a high concentration,and this region is called the LDD region.

For example, Japanese Patent No. 2564725 discloses a method ofmanufacturing a TFT having an LDD region. In this method, a gateinsulating film is formed widely in the direction of a channel widthfrom a gate electrode, and an insulating film thinner than the gateinsulating film is further formed beside this gate insulating film. Thenby utilizing the difference in the thickness between this insulatingfilm and the gate insulating film, an LDD region is formed in asemiconductor film between the end portion of the gate electrode and asource or drain region.

Moreover, as means for preventing deterioration caused by a hot carrier,a so-called GOLD (Gate-drain Overlapped LDD) structure is known in whichthe LDD region is arranged so as overlapping the gate electrode via thegate insulating film. With a structure of this kind, the high electricfield in the vicinity of a drain is relaxed to prevent hot carrierimplantation, which is effective for prevention of the deteriorationphenomenon. For example, though a GOLD structure formed by a side wallwhich is formed of silicon is disclosed by Mutuko Hatano, Hajime Akimotoand Takeshi Sakai, in “IEDM97 TECHNICAL DIGEST, p 523-526, 1997,” it hasbeen confirmed that an extremely excellent reliability can be achievedwhen compared with TFTs of other structures.

It had been preferred that the introduction of an impurity element tothe semiconductor layer, which is used to form an impurity region suchas the LDD region, the source or drain region of the TFT having such astructure, be conducted in a self-aligning manner utilizing the gateelectrode and the insulating film for a mask provided on thesemiconductor layer. Furthermore, in order to reduce the number ofmasks, a method (referred as cross dope method in the present invention)has been employed in which once an impurity element of a one conductivetype is introduced into the whole surface by utilizing the gateelectrode and the insulating film as a mask, an impurity element of aconductive type opposite the one conductive type is introduced into theimpurity region of a TFT of either the P-channel TFT or the N-channelTFT at a high concentration.

However, the characteristics being demanded for the pixel TFT and theTFT of the drive circuit such as a shift resist circuit, or a buffercircuit are not necessarily the same. For example, in the pixel TFT, alarge reversal bias (negative voltage in an N-channel TFT) is applied toa gate, whereas the TFT of the drive circuit basically does not operatein the reversal bias state. Also, the operating velocity of the pixelTFT can be 1/100 of less than that of the TFT of the drive circuit.

The GOLD structure is highly effective in preventing the deteriorationof the on-current value, but on the other hand, there arises a problemin that the off-current becomes higher compared with the structure of anormal LDD. Therefore, the GOLD structure was not a preferred structurefor applying to the pixel TFT. Contrarily, although the structure of anormal LDD is highly effective in suppressing the off-current value, ithas a low effect in relaxing the electric field in the vicinity of adrain and in preventing deterioration caused by the hot carrierimplantation. In this way, in a semiconductor device such as the activematrix liquid crystal display device that has a multiple of integratedcircuits of different operating conditions, it was not always desirableto form all the TFTs with the same structure. Such a point of issue likehas been revealed as an enhanced characteristic is required for thecrystalline silicon TFT in particular, and as the performance demandedof the active matrix liquid crystal display device becomes increased.

Furthermore, although there are several means to decrease theoff-current value of the TFT, it was necessary to form a good junctionof the channel forming region and the impurity region (LDD region,source region or drain region). In order to do this, the distribution ofan impurity element in the interface of the channel forming region andthe impurity region that contacts the channel forming region needs to beaccurately controlled. However, when the above-mentioned cross dopemethod is implemented, the distribution of an impurity element in theinterface was difficult to control accurately since an impurity elementof a one conductive type and an impurity element of a conductive typeopposite the one conductive type were introduced into the impurityregion of the TFT on one side.

This type of LDD structure is formed by focusing on the characteristicof the N-channel TFT. Many of the P-channel TFTs, which are formed onthe same substrate to form the CMOS circuit or the like, were formed asa single drain structure for the purpose of lessening the number ofmasks as much as possible. In this case, there arises a problem in thatsince phosphorous (P) for forming an LDD in the N-channel TFT is dopedinto the source or drain region in the P-channel TFT, a defect is formedin the junction with the channel forming region and the off-currentvalue increases.

SUMMARY OF THE INVENTION

A technique of the present invention is for solving the above problems,and therefore it is an object of the present invention to provide a TFT,which is to be arranged in every circuit of the semiconductor device,having an appropriate structure in accordance with a function of acircuit, to thereby improve operating characteristics and reliability ofa semiconductor device.

In order to solve the above problems, according to one aspect of thepresent invention, there is provided a semiconductor device having apixel TFT formed in a display region and a TFT of a drive circuit formedin the periphery of the display region on the same substrate,characterized in that: each of the pixel TFT and the TFT of drivecircuit has an active layer, an LDD region formed in the active layer, agate insulating film provided between the active layer and thesubstrate, and a gate electrode provided between the gate insulatingfilm and the substrate; at least a portion of each LDD region in thepixel TFT or an N-channel TFT of the drive circuit is arranged so as tooverlap with the gate electrode; and an LDD region in a P-channel TFT ofthe drive circuit is arranged so as to overlap with a gate electrode inthe P-channel TFT. Also, it is preferable that an LDD region in each ofthe pixel TFT and the N-channel TFT of the drive circuit is arranged soas not to overlap with a channel protection insulating film, and tooverlap with a gate electrode by at least a portion thereof; and an LDDregion in a P-channel of the drive circuit is arranged so as to overlapwith a channel protection insulating film in the P-channel 1 of thedrive circuit, and to overlap with a gate electrode in the P-channel.

Further, according to another aspect of the present invention, aP-channel TFT of the drive circuit has a first impurity regioncontaining therein both an impurity element that gives p-type and animpurity element that gives n-type and a second impurity regioncontaining therein an impurity element that gives p-type, and ischaracterized in that the second impurity region is formed between thefirst impurity region and an LDD region in the P-channel TFT of thedrive circuit.

This is so constructed that phosphorous that is doped into a source ordrain region of a P-channel TFT is not doped into the junction with thechannel forming region without increasing the number of masks, attaininga reduction of an off-current value.

A storage capacitor connected to the pixel TFT includes a capacitorwiring formed over the substrate, an insulating film formed on thecapacitor wiring, and a semiconductor layer formed on the insulatingfilm. Alternatively, an organic resin film is formed on the pixel TFT,and a capacitor includes a light shielding film formed on the organicresin film, a dielectric film formed closely to the light shieldingfilm, and a pixel electrode connected to the pixel TFT, a portion ofwhich overlaps with the light shielding film.

Moreover, in order to solve the above problems, the present inventionprovides a method of manufacturing a semiconductor device having a pixelTFT formed in a display region and a TFT of a drive circuit formed inthe periphery of the display region on the same substrate, the methodcomprising the steps of: forming an LDD region in the pixel TFT or anN-channel TFT of the drive circuit at least a portion of which overlapswith a gate electrode; and forming an LDD region in a P-channel TFT ofthe drive circuit that overlaps a gate electrode in the P-channel TFT.Further, the method may comprises the steps of: forming an LDD region inthe pixel TFT and an N-channel TFT of the drive circuit so as not tooverlap with a channel protection insulating film, and to overlap with agate electrode by at least a portion thereof; and forming an LDD regionin a P-channel TFT of the drive circuit in a manner so as to overlapwith a channel protection insulating film in the P-channel TFT, and tooverlap with the gate electrode in the P-channel 1.

The above method of manufacturing a semiconductor device furthercomprises the step of: forming a first impurity region containingtherein both an impurity element that gives p-type and an impurityelement that gives n-type therein and a second impurity regioncontaining therein an impurity element that gives p-type therein in theP-channel TFT of the drive circuit, and the second impurity region ispreferably formed between the first impurity region and an LDD region inthe P-channel TFT of the drive circuit.

Further, according to another aspect of the present invention, a methodof manufacturing a semiconductor device having a pixel TFT formed in adisplay region and a TFT of a drive circuit formed in the periphery ofthe display region on the same substrate is characterized in that themethod comprises: a first step of forming gate electrodes on asubstrate; a second step of forming a gate insulating film on the gateelectrodes; a third step of semiconductor layers on the gate insulatingfilm; a fourth step of forming channel protection films on thesemiconductor layers; a fifth step of introducing an impurity elementthat gives n-type into the semiconductor layers, and forming LDD regionsin an N-channel TFT that does not overlap with the channel protectionfilms; a sixth step of introducing an impurity element that gives n-typeinto the semiconductor layers, and forming a source region or a drainregion on the N-channel TFT; and a seventh step of introducing animpurity element that gives p-type into one of the semiconductor layers,and forming an LDD region, and a source region or a drain region in theP-channel TFT that overlaps with the channel protection film.

The above method of manufacturing a semiconductor device ischaracterized by further comprising the steps of: forming a capacitorwiring on the substrate; forming an insulating layer on the capacitorwiring; forming a semiconductor layer on the insulating layer; andforming a storage capacitor connected to the pixel TFT. The methodfurther comprises the steps of: forming an organic resin film on thepixel TFT; forming a light shielding film on the organic resin film;forming a dielectric film on the light shielding film; and forming apixel electrode connected to the pixel TFT, a portion of which overlapswith the light shielding film; forming a capacitor therefrom. The lightshielding film is formed of one or plural kinds of materials selectedfrom aluminum, tantalum, and titanium, and the dielectric film ispreferably formed of an oxide of a material which the light shieldingfilm is formed of. Most preferably, this oxide is formed by anodicoxidation.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects of the subject invention will become more fullyapparent as the following description is read in light of the attacheddrawings wherein:

FIGS. 1A-1C are diagrams illustrating a manufacturing process of a pixelTFT and a TFT of a drive circuit of Embodiment 1;

FIGS. 2A-2C are diagrams illustrating a manufacturing process of a pixelTFT and a TFT of a drive circuit of Embodiment 1;

FIG. 3 is a diagram illustrating a manufacturing process of a pixel TFTand a TFT of a drive circuit of Embodiment 1;

FIG. 4 is a diagram illustrating a manufacturing process of a pixel TFTand a TFT of a drive circuit of Embodiment 2;

FIGS. 5A-5C are diagrams illustrating a manufacturing process of acrystalline semiconductor film of Embodiment 3;

FIGS. 6A-6C axe diagrams showing an example of a sectional structure ofa storage capacitor of Embodiment 4;

FIGS. 7A-7B are diagrams showing an example of a sectional structure ofa storage capacitor of Embodiment 4;

FIG. 8 is a diagram showing a sectional structure of an active matrixliquid crystal display, device of Embodiment 7;

FIG. 9 is a perspective view schematically showing an active matrixliquid crystal display device of Embodiment 7;

FIG. 10 is a diagram of the top surface of a pixel of Embodiment 7;

FIGS. 11A-11F are diagrams illustrating examples of a semiconductordevice of Embodiment 8;

FIGS. 12A-12C are diagrams illustrating a manufacturing process of apixel TFT and a TFT of a drive circuit of Embodiment 6; and

FIG. 13 is a diagram illustrating a manufacturing process of a pixel TFTand a TFT of a drive circuit of Embodiment 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiment modes of the present invention will beexplained in detail as indicated in the following embodiments.

Embodiment 1

A description of a preferred embodiment of the present invention will begiven with reference to FIGS. 1A through 3. Here, a description of amethod of simultaneously manufacturing a pixel TFT in a display regionand a TFT of a drive circuit formed in the periphery of the displayregion will be explained in detail by following a process.

In FIG. 1A, a low alkali, glass substrate or a quartz substrate can beused as a substrate 101. On the surface of the substrate 101 where a TFTis formed, an insulating film such as a silicon oxide film, a siliconnitride film, or a silicon oxide nitride film can be formed (not shown).Gate electrodes 102 through 104 and a capacitor wiring 105 are formed byemploying materials containing an element selected from tantalum (Ta),titanium (Ti), tungsten (W), molybdenum (Mo), and aluminum (Al) orhaving one of these elements as a main component and are coated byutilizing well-known film formation methods such as sputtering andvacuum evaporation. Then, etching and patterning is carried out so thatthe end surface is tapered. For example, after forming the Ta film at athickness of 200 nm by sputtering, and forming a resist mask into apredetermined shape, a plasma etching is performed with mixed gas of CF₄and O₂ to make a desired shape. Also, a gate electrode can be atwo-layer structure (not shown) composed of tantalum nitride (TaN) andTa, or tungsten nitride (WN) and W. Although not shown in the figures, agate wiring connected to the gate electrode is formed at the same time.

A gate insulating film 106 is formed of a material having a siliconoxide and silicon nitride as constituents at a thickness of 10 to 200nm, preferably 50 to 150 nm. For example, a laminated layer formed of asilicon nitride film 106 a made of SiH₄, NH₃, and N₂ as raw materialshaving a thickness of 50 nm having and a silicon oxide nitride film 106b with a thickness of 75 nm having SiH₄ and N₂O as raw material byplasma CVD can be the gate insulating film. Of course, the gateinsulating film 106 can be a single layer made up of a silicon nitridefilm or a silicon oxide film. Further, in order to obtain a cleansurface, it is better to implement plasma hydrogenate before forming thefilm of the gate insulating film.

Next, the formation of a crystalline semiconductor film that becomes anactive layer of a TFT is performed. Silicon is used as the material forthe crystalline semiconductor film. First, an amorphous silicon film isformed at a thickness of 20 to 150 nm by a well-known film formationmethod such as plasma CVD or sputtering so as to be close to the gateinsulating film 106. Although the manufacturing conditions of anamorphous silicon film is not restricted by anything, it is desired thatthe concentration of impurity elements of oxygen and nitrogen containedin the film be reduced to 5×10¹⁸ cm⁻³ or less. Since the gate insulatingfilm and the amorphous silicon film can be formed with the same filmformation method, both may be continuously formed. After forming thegate insulating film, contamination on the surface can be prevented bynot exposing it in the atmosphere once and characteristic unevenness andfluctuation of a threshold voltage of a TFT manufactured can be reduced.A crystalline silicon film 107 is thereafter formed by employing awell-known crystallization technique. For example, the crystallinesilicon film 107 can also be formed by a crystallization method using acatalytic element such as laser crystallization, or thermalcrystallization (solid phase crystallization), or by following atechnique disclosed in Japanese Patent Application Laid-Open No. Hei7-130652.

In the region where the N-channel of the crystalline silicon film 107 isformed, boron (B) may be added at a level of approximately 1×10¹⁶ to5×10¹⁷ cm⁻³ in order to control a threshold voltage. The adding of boron(B) may be implemented by an ion dope method or may be added at the sametime when forming the amorphous silicon film (FIG. 1A).

Next, the adding of an impurity element that gives n-type is performedfor the purpose of forming an LDD region in the N-channel TFT. First, amask insulating film 108 made of a silicon oxide film and a siliconnitride film is formed at a thickness of 100 to 200 nm, typically 120nm, on the surface of the crystalline silicon film 107. And aphotoresist film in entirely formed on this surface. Thereafter, thephotoresist film is exposed using gate electrodes 102 through 104 asmasks by an exposure from the back surface of the substrate 101 tothereby form resist masks 109 through 112. Through this method, resistmasks can be formed on the gate electrodes and within the gateelectrodes.

Then, an impurity element that gives the n-type is doped via the maskinsulating film 108 into the crystalline silicon film underlying it byan ion doping method (an ion implantation method can also be used). Inthe technical field of semiconductors, applicable impurity elements thatgive n-type include the elements from the periodic table group 15 suchas phosphorous (P), arsenic (As), and antimony (Sb). In this case,phosphorous (P) is used. The concentration of phosphorous (P) added intoimpurity regions 113 through 118 that are thus formed is preferably inthe range of 1×10¹⁷ to 5×10¹⁸ cm⁻³, and here, it is 5×10¹⁷ cm⁻³. Thepresent invention expresses the concentration of the impurity elementthat gives n-type included in the impurity regions 113 through 118 as“n” (FIG. 1B).

Next, the mask insulating film 108 is removed by etching using thisresist mask and channel protection films 119 through 122 are formed. Forthe purpose of conducting a better choice of etching the mask insulatingfilm 108 with respect to the crystalline silicon film 107 as anunderlying film, a wet etching method using fluorine solution is adoptedhere. Of course, dry etching can be implemented, for instance, theinsulating film 108 may be etched by using CHF₃. In any case, theprocess here is to conduct over-etching so that the channel protectionfilms 119 through 122 can be formed further inside than the end surfaceof the resist masks 109 through 112 (FIG. 1C).

A process of forming an impurity region to function as a source regionor a drain region in the N-channel TFT is performed next. In thisprocess, masks 123 through 125 are formed by a normal exposure methodusing a resist. Then, the channel protection film 122 on the capacitorwiring 105 is etched and removed by using the thus formed resist masks.Subsequently, impurity regions 126 through 130 into which an impurityelement that gives n-type has been added are formed by an ion dopingmethod (an ion implantation method can also be used) on the crystallinesilicon film 107. Here, in the impurity regions 126 through 130, theimpurity element is included at a concentration of 5×10²⁰ cm⁻³, thoughit can be 1×10²⁰ to 1×10²¹ cm⁻³. The present invention expresses thisconcentration as “n⁺” (FIG. 2A).

A process of adding an impurity element that gives p-type is performedfor the purpose of forming a source region or a drain region in theP-channel TFT of the drive circuit. In the technical field ofsemiconductors, applicable semiconductor elements that give p-typeinclude the element from the periodic table group 13 such as boron (B),aluminum (Al), and gallium (Ga), and here, boron is used. A mask 131 isformed so that it is positioned on the inside of the channel protectionfilm 119, and resist masks 132 and 133 are formed so as to cover theentire region where the N-channel TFTs are formed. Impurity regions 134though 136 are thereafter formed by an ion doping method (an ionimplantation method can also be used) using diborane (B₂H₆). An impurityelement is added from the surface of the crystalline silicon film intothe impurity regions 135 a, 135 b, 136 a and 136 b. The concentration ofboron in the regions is in the range of 1.5×10²⁰ to 3×10²¹ cm⁻³, here itis 2×10²¹ cm⁻³. The present invention expresses the concentration of theimpurity element that gives p-type included in the impurity regions 135a, 135 b, 136 a, and 136 b as “p⁺”. On the other hand, since thecrystalline silicon film is added with an impurity element via thechannel protection film 119, the concentration of boron (B) became1×10¹⁶ to 1×10¹⁸ cm⁻³ in this impurity region 134. The present inventionexpresses the concentration of the impurity element that gives p-typeincluded in the impurity region 134 that is thus formed in this processas “p⁻”.

As shown in FIGS. 1B to 2A, the impurity regions 135 b and 136 b areadded with phosphorous (P) in the previous process, and therefore aregion containing a mixture of boron (B) and phosphorous (P) is formed.However, by adding boron (B) at a concentration of 1.5 to 3 times higherin this process, p-type conductivity can be secured and no influence isinflicted upon the characteristics of the TFT. The present inventionindicates these regions as an impurity region “B”. Also, the impurityregions 135 a and 136 a at the side of the channel forming region of theimpurity regions “B” 135 b and 136 b contain boron (B) only, and thepresent invention indicates these regions as an impurity region “A”. Theimpurity region 134 overlapping the gate electrode 103 as well as thechannel protection film 120 is also formed as a region containing boron(B) only and functions as an LDD region (FIG. 2B).

Respective impurity elements are selectively added into the crystallinesilicon film and then etching is carried out on this crystalline siliconfilm so that it is divided into island-like films. Then a protectioninsulating film 137, which will later become a portion of a firstinterlayer insulating film, is formed. The protection insulating film137 can be formed of a silicon nitride film, a silicon oxide film, asilicon oxide nitride film, or a lamination film of the combinationthereof and may be at a thickness of 100 to 400 nm.

Thereafter, the heat treatment process is carried out for the purpose ofactivating the impurity elements giving either an n-type or p-type thathave been doped at respective concentrations. This process can becarried out by annealing methods such as furnace annealing, laserannealing, or rapid thermal annealing (RTA). Here, activation is carriedout by furnace annealing. Heat treatment is performed at 300 to 650° C.,preferably 500 to 550° C. in a nitrogenic atmosphere. In this process,heat treatment was performed at 525° C. for 4 hours. Then heat treatmentis further performed at 300 to 450° C. for 1 to 12 hours in anatmosphere containing 3 to 100% of hydrogen and then hydrogenation iscarried out on the active layer. This process is to terminate thedangling bonds in the active layer by thermally excited hydrogen. Asother hydrogenation means, plasma hydrogenation (using hydrogen excitedby plasma) can be performed.

When the crystalline silicon film 107, which becomes the active layer,is fabricated by a crystallization method using a catalytic element froman amorphous silicon film, the amount of catalytic element remaining inthe crystalline silicon film 107 is approximately 1×10¹⁷ to 5×10¹⁹ cm⁻³.Of course, there is no problem in completing and operating the TFT inthis situation. However, it is more preferable that the residualcatalytic element be removed at least from the channel forming region.One of the means of removing this catalytic element is to utilize thegettering action of phosphorous (P). The concentration of phosphorous(P) necessary in the gettering process is approximately the same as thatof impurity region (n⁺) formed in FIG. 2B. Through the heat treatment inthe activation process that is implemented here, the catalytic elementcan be gettered from the channel forming region in the N-channel TFT andthe P-channel TFT to the impurity regions in the periphery wherephosphorous (P) has been doped. As a result, the concentration of thecatalytic element in the channel forming region can be made to be 5×10¹⁷cm⁻³ or less. The catalytic element having a concentration of 1×10¹⁸ to5×10²⁰ cm⁻³ has segregated to the above impurity region (FIG. 2C).

After completing the activation process, an interlayer insulating film138 is formed at a thickness of 500 to 1500 nm on the protectioninsulating film 137. A first interlayer insulating film is a laminationfilm formed of the above protection insulating film 137 and theinterlayer insulating film 138. A contact hole that reaches the sourceregion or drain region of the respective 11 is formed, and then sourcewirings 139 through 141 and drain wirings 142 and 143 are formed.Although not shown in the figure, this electrode according to thepresent embodiment is laminated film of a 3-layered structure formed ofa 100 nm Ti film, a 300 nm aluminum film containing Ti, and a 150 nm Tifilm by sputtering in successions.

The protection insulating film 137 and the interlayer insulating film138 can be formed of a silicon nitride film, a silicon oxide film or asilicon oxide nitride film, or the like. In any case, it is better thatthe internal stress of the film be made into the compression stress.

Next, using a silicon nitride film, a silicon oxide film, or a siliconoxide nitride film, a passivation film 144 is formed at a thickness of50 to 500 nm (typically 100 to 300 nm). If hydrogenation process iscarried out in this state, desirable effects can be achieved withrespect to an improvement in the characteristics of TFTs. For instance,it is appropriate that heat treatment is performed at 300 to 450° C. inan atmosphere containing 3 to 100% of hydrogen for 1 to 12 hours orsimilar effects can be obtained if a plasma hydrogenation methodemployed. Moreover, at the position of forming a contact hole forconnecting a pixel electrode to the drain wiring in a later process, anopening portion can be formed in the passivation film 144.

Then a second interlayer insulating film 145 formed of an organic resinfilm is formed at about 1 ìm of thickness. Polyimide, acryl, polyamide,polyimide-amide, BCB (benzocyclobutene), etc. are applicable asinorganic resin materials. Here, after coating the substrate, the secondinterlayer insulating film 145 is formed by baking at 300° C. using atype of polyimide that is thermal polymeric. Then, a contact hole thatreaches the drain wiring 143 is formed in the second interlayerinsulating film 145 and the passivation film 144, on to which a pixelelectrode 146 is provided. If the pixel electrode 146 is used intransmission type liquid crystal display devices, a transparentconductive film can be used. On the other hand, if it is used inreflection type liquid crystal display devices, a metallic film can beused. Here the pixel electrode is used in a transmission type liquidcrystal device; therefore an indium tin oxide (ITO) film is formed at athickness of 100 nm by sputtering. A pixel electrode 190 is theelectrode of a neighboring pixel.

Through the above processes, the pixel in a display region and the TFTof the drive circuit in the periphery of the display region can beformed on the same substrate. In the drive circuit, an N-channel TFT 168and a P-channel TFT 167 are formed, allowing for a logic circuitstructured with a CMOS circuit as the basic circuit. A pixel TFT 169 isan N-channel TFT, and furthermore, from the capacitor wiring 105, asemiconductor layer 166, and an insulating layer formed therebetween, astorage capacitor 170 is connected to this pixel 169 (FIG. 3).

A P-channel TFT 167 of the drive circuit has a channel forming region147, source regions 150 a and 150 b, drain regions 151 a and 151 b, andLDD regions 148 and 149. The source region 150 b and the drain region151 b are formed as the impurity region “B”. The concentration of boron(B) in this region is 1.5 to 3 times higher than the concentration ofphosphorous (P). On the inside of the impurity region “B”, that is, thesource region 150 a and the drain region 151 a formed on the side of thechannel forming region 147 correspond to the impurity region “A”. Thisimpurity region “A” is a region containing only boron at the sameconcentration as that of the impurity region “B”. Further, the LDDregions 148 and 149 overlapping the gate electrode 102 as well as thechannel protection film 119 are also formed as regions containing onlyboron (B). By separating the impurity region “B” from the channelforming region in this way, the reliable junctions between N-channelforming region and the LDD region that comes in contact with the channelforming region, and still further between the LDD region and either thesource region or the drain region are attained, enabling thecharacteristics of the P-channel TFT well retained.

An N-channel 168 of the drive circuit has a channel forming region 152,a source region 155 and a drain region 156, and LDD regions 153 and 154.The pixel TFT 169 has channel forming regions 157 and 158, sourceregions or drain regions 163 through 165, and LDD regions 159 through162. The LDD regions in the N-channel TFT of the drive circuit areprovided for the principal purpose of relaxing a high electric field inthe vicinity of the drain to prevent the deterioration of the on-currentvalue due to hot carrier implantation. Thus, it is appropriate to setthe concentration of a suitable impurity element that gives n-type to5×10¹⁷ to 5×10¹⁸ cm⁻³. On the other hand, the LDD regions in the pixelTFT are provided for the principal purpose of decreasing the off-currentvalue, in which the concentration of the impurity element can be thesame as that in the LDD regions in the N-channel of the drive circuit,although it can also be ½ to 1/10 of that concentration. In FIG. 3,although the pixel TFT 169 is completed as a double-gate structure, itcan also be a single-gate structure, or a multi-gate structure providedwith a plurality of gate electrodes.

As explained above, according to the present invention, the structure ofthe TFT constituting each circuit has been optimized in accordance withthe specifications demanded by the pixel TFT and the driver circuit,with the result that the operating efficiency and reliability of asemiconductor device can be improved.

Embodiment 2

Referring to FIG. 4, Embodiment 2 is explained by way of example inwhich a storage capacitor connected to the pixel TFT is provided, as isdifferent from Embodiment 1. The P-channel TFT 167 and the N-channel TFT168 of the drive circuit and the pixel TFT 169 are manufactured in thesame way as in Embodiment 1. The point of difference from Embodiment 1will be explained hereinbelow.

At least on the tope of the pixel TFT, a light shielding film 171 isformed on the second interlayer insulating film 145. The light shieldingfilm 171 is a film formed of one or a plurality of elements selectedfrom Al, Ti, and Ta or has one of these elements as main components witha thickness of 100 to 300 nm, and is patterned into a predeterminedshape. Similar to the second interlayer insulating film, a thirdinterlayer insulating film 172 is formed at a thickness of 0.5 to 1 μmon the light shielding film 171 using an organic resin film. A contacthole that, reaches the drain wiring 143 is formed in the thirdinterlayer insulating film 172, the second interlayer insulating film145, and the passivation film 144, on to which a pixel electrode 173 isthen provided. If the pixel electrode 173 is used in transmission typeliquid crystal display devices, a transparent conductive film can beused. On the other hand, if it is used in reflection type liquid crystaldisplay devices, a metallic film can be used. Here, since the pixelelectrode is used in a transmission type liquid crystal device, anindium tin oxide (ITO) film is formed at a thickness of 100 nm bysputtering. In this way, the storage capacitor 174 connected to thepixel TFT 169 can be formed from the light shielding film 171, the thirdinterlayer insulating film 172, and the pixel electrode 173.

Embodiment 3

A process of forming a crystalline semiconductor film that becomes anactive layer of the TFT indicated in embodiments 1 and 2 will beexplained in this embodiment with reference to FIG. 5A-5C. First, gateelectrodes 1102 and 1103 are formed at a thickness of 100 to 400 nm on asubstrate 1101 (a glass substrate in this embodiment). Each of the gateelectrodes is faulted of a material containing one or a plurality ofelements selected from Al, Ti, Ta, Mo, and W, and is patterned andformed so that the end surface will be taper-like. Although not shown,the gate electrode can also be a laminated structure formed of the abovematerial(s). For instance, it can be a 2-layered structure of tantalumnitride (TaN) and Ta from the substrate side. Further, an oxide can becoated and formed by anodic oxidation and the like on the surface of thegate electrode. A gate insulating film 1104 is formed of a siliconnitride film, a silicon oxide film, or a silicon oxide nitride film at athickness of 20 to 200 nm, preferably 75 to 125 nm. Then, on the gateinsulating film 1104, a 50 nm thickness of amorphous semiconductor film1105 (an amorphous silicon film in this embodiment) is formedcontinuously without being released into the atmosphere.

Thereafter, a water solution containing 10 ppm of catalytic element(nickel in this embodiment) in terms of a weight is coated by a spincoating method to form a catalytic element-contained layer 1106 on theentire surface of the amorphous semiconductor film 1105. The catalyticelements that are usable in this embodiment include germanium (Ge), iron(Fe), palladium (Pd), tin (Sn), lead (Pb), cobalt (Co), platinum (Pt),copper (Cu), and gold (Au) other than nickel (Ni). According to thisembodiment, nickel is added by the spin coating method. Other than theabove, means for forming a thin film made of a catalytic element (anickel film in this embodiment), on the amorphous semiconductor film bya vapor method or sputtering can also be employed. (FIG. 5A)

Before crystallization, heat treatment is performed at 400 to 500° C.for about 1 hour. After eliminating hydrogen from the inside of thefilm, heat treatment is performed at 500 to 650° C. (preferably at 550to 570° C.) for 4 to 12 hours (preferably for 4 to 6 hours). In thisembodiment, heat treatment is performed at 550° C. for 4 hours and acrystalline semiconductor film 1107 (a crystalline silicon film in thisembodiment) is formed. (FIG. 5B)

Regarding the active layer 1107 formed in the above manner, by using acatalytic element (here it is nickel) to promote crystallization, acrystalline semiconductor film having excellent crystal qualities can beformed. Moreover, to enhance the crystal qualities, an lasercrystallization method can be used together. For instance, an XeFexcimer laser light (a wavelength of 308 nm) is used to irradiate thecrystalline semiconductor film 1107 fabricated in FIG. 5B with a linearbeam at an oscillation frequency of 5 to 50 Hz and at an energy densityof 100 to 500 mJ/cm² so as to set the overlap ratio of the linear beamat 80 to 98%. As a result, a crystalline semiconductor film 1108 withfurther excellent crystal qualities can be formed. (FIG. 5C)

By utilizing the crystalline semiconductor film fabricated in this wayon the substrate 1101, a TFT with good characteristics can be obtainedwhen manufactured by the procedures indicated in embodiments 1 and 2.The characteristics of a TFT can be typically expressed by the electricfield effect mobility. Therefore the characteristics of a TFT formed ofthe crystalline semiconductor film fabricated by the present inventioncan be obtained in which the electric field effect mobility in theN-channel TFT and the P-channel TFT are 150 to 220 cm²/V·sec and 90 to120 cm²/V·sec, respectively. Besides, little characteristicdeterioration can be observed even if the TFT is operated continuouslyand excellent characteristics can also be achieved in view of areliability perspective.

Embodiment 4

In this embodiment, another structure in which a storage capacitorconnected to the pixel TFT will be explained with reference to FIGS. 6Ato 7B. Here, the processes of forming the storage capacitor shown inFIGS. 6A to 7B are similar with those explained in Embodiment 1. Thatis, the processes up to the formation of the second interlayerinsulating film 145 made of an organic resin film in this embodiment arethe same as those in Embodiment 1, and these processes have beendescribed with reference FIGS. 1A to 3. Hence, the explanation in thisembodiment will be given focusing on the point of difference withEmbodiment 1.

In FIG. 6A, firstly, the second interlayer insulating film 145 is formedby following the process of Embodiment 1, and then a light shieldingfilm 301 is formed of a material containing an element selected from Al,Ta, and Ti. Next, a dielectric film 302 (formed of an oxide from amaterial which forms the light shielding film) is formed at a thicknessof 30 to 150 nm (preferably 50 to 75 nm) on the surface of the lightshielding film 301 by anodic oxidation.

When forming the dielectric film 302 by anodic oxidation, first, atartaric acid ethylene glycol solution of a sufficiently small alkaliion concentration is prepared. This solution is a mixture of 15% oftartaric acid ammonium water solution and ethylene glycol in theproportion of 2:8. Ammonia water is added to this solution and thenadjustments are made so that the pH will become 7±0.5. Then, a platinumelectrode that becomes a cathode is placed in this solution. Thesubstrate on which the light shielding film 301 is formed is immersed inthe solution, and then using the light shielding film 301 as an anode, adirect current is applied thereto at a constant level (several mA toseveral tens mA). The voltage between the anode and the cathode in thesolution is time-varying along with the growth of the oxide, but thevoltage is adjusted so that the current may be constant. When thevoltage reaches 150 V, the oxidation process is completed without havingto maintain the voltage or with the retention time in a range of severalseconds to several tens seconds. In doing this, the dielectric film canbe formed without wrapping of the surface where the light shielding film301 comes in contact with the second interlayer insulating film.

In the present embodiment, a dielectric film is formed only on thesurface of the light shielding film, but a vapor phase method such asplasma CVD, thermal CVD, or sputtering can be employed to form thedielectric film. In that case preferably the film thickness is also 30to 150 nm (preferably 50 to 75 nm). Also, a silicon oxide film, asilicon nitride film, a silicon oxide nitride film, a DLC (diamond likecarbon) film, or an organic resin film, or a lamination film combiningthese can be used as the dielectric film.

A pixel electrode 303 is thereafter formed in the same way as that ofembodiment 1. In this way, a storage capacitor 304 can be formed on theregion in which the light shielding film 301 overlaps the pixelelectrode 303 via the dielectric film 302.

In the structure of FIG. 6B, after forming the light shielding film 301and the dielectric film 302 in the same way as that of FIG. 6A, a spacer305 made of organic resin is formed. A film made of a material selectedfrom polyimide, polyamide, polyimide-amide, acrylic, BCB(benzocyclobutene) can be used as an inorganic resin film. Next, thespacer 305, the second interlayer insulating film 145, and thepassivation film 143 are etched to form a contact hole, and a pixelelectrode 306 is formed of the same material as that of embodiment 1. Inthis way, a storage capacitor 307 can be formed on the region in whichthe light shielding film 301 overlaps the pixel electrode 306 via thedielectric film 302. Providing the spacer 305 can prevent the shortcircuit that may be generated between the light shielding film 301 andthe pixel electrode 306.

In the structure of FIG. 6C, the light shielding film 301 is formed inthe same way as that of FIG. 6A and a spacer 308 made of organic resinis formed so as covering the end portion of the light shielding film301. A film mad of a material selected from polyimide, polyamide,polyimide-amide, acrylic, BCB (benzocyclobutene) can be used as aninorganic resin film. Next, a dielectric film 309 is formed on thesurface of the light shielding film 301 that is exposed by anodicoxidation. No dielectric film is formed in the portion that comes incontact with the spacer 308. Next, the spacer 308, the second interlayerinsulating film 145, and the passivation film 143 are etched to form acontact hole, and a pixel electrode 310 is formed of the same materialas that of embodiment 1. In this way, a storage capacitor 311 can beformed on the region in which the light shielding film 301 overlaps thepixel electrode 310 via the dielectric film 309. Providing the spacer308 can prevent short circuit that may be generated between the lightshielding film 301 and the pixel electrode 310.

In FIG. 7A, the second interlayer insulating film 145 is formed first byfollowing the process in Embodiment 1 and then an insulating film 312formed of materials such as a silicon oxide film, a silicon nitridefilm, or a silicon oxide nitride film is formed thereon. A known filmformation method is used to form the insulating film 312, although it isbetter to use sputtering in particular. Hereinafter, the light shieldingfilm, the dielectric film, and the pixel electrode are formed in thesame way as that in FIG. 6A and then a storage capacitor 313 isprovided. Providing the insulating film 312 improves adhesion with theunderlayer of the light shielding film and the dielectric film can beprevented from wrapping the interface with the underlayer of the lightshielding film when the dielectric film is formed by anodic oxidation.

In FIG. 7B, after forming the insulating film and the light shieldingfilm in the same way, the region that is not close to the lightshielding film of the insulating film is removed by etching to form aninsulating film 314 so that it overlaps under the light shielding film.Next, a pixel electrode 315 is provided. With this structure, theadhesion of the light shielding film with the underlayer thereof can beimproved and the dielectric Min can be prevented from wrapping theinterface with the underlayer of the light shielding film can beprevented when the dielectric film is formed by anodic oxidation.Furthermore, the transmission rate of the light through the pixel regionin which the light shielding film is formed can be improved.

It is possible to combine the structures shown in FIGS. 7A and 7B withthe structures shown in FIGS. 6B and 6C in which a spacer is provided.It is further possible to combine the structures according to thepresent embodiment shown in FIGS. 6A to 7B with the structures accordingto embodiment 1 and embodiment 2.

Embodiment 5

In a method of manufacturing a semiconductor device provided with apixel TFT in a display region shown in Embodiments 1 and 2 and a TFT ofa drive circuit formed in the periphery of the display region on thesame substrate, a crystalline semiconductor film as an active layer,insulating films such as a gate insulating film, an interlayerinsulating film, and an underlying film, and conductive films such as agate electrode, a source wiring, a drain wiring, and a pixel electrodecan all be manufactured by sputtering. The advantage of employing thesputtering method is that when forming a conductive film, the DC (directcurrent) discharge method can be adopted. Hence, it is applicable forforming a uniform film on a large-area substrate. Further, it is notnecessary to use a silane (SiH₄) which needs to be handled with greatcaution when forming films made of silicon-based materials such as anamorphous silicon film and a silicon nitride film. Thus, safety ofoperation can be secured. This matter can be utilized as a great meritespecially for a production site. Hereinafter, a manufacturing processemploying the sputtering method will be explained following theprocesses of Embodiment 1.

The gate electrodes 102 through 104 and the capacitor wiring 105 in FIG.1A can be easily formed by the known sputtering method using targetmaterials such as Ta, Ti, W, and Mo. When using compound materials suchas W—Mo and Ta—Mo, similarly, it is appropriate to use compounds oftarget materials. Further, in case of forming TaN and WN, the above canbe manufactured by appropriately adding elements such as nitrogen (N₂)and ammonia (NH₃) other than argon (Ar) in a sputtering atmosphere.Also, in addition to argon (Ar), there is a method of controlling theinternal stress of a film that is to be manufactured by adding helium(He), krypton (Kr), and xenon (Xe) to the gas for sputtering.

The silicon nitride film 106 a used in the gate insulating film 106 canbe formed by using silicon (Si) target and appropriately mixing Ar, N₂,hydrogen (H₂), and NH₃, or even by using a target material of siliconnitride, the silicon nitride film can be formed in the same way. UsingSi target and appropriately mixing Ar, N₂, H₂, and N₂O, the siliconoxide nitride film 106 b can be manufactured by sputtering.

In the same way, Si target is used so that the amorphous silicon filmcan be manufactured by utilizing Ar and H₂ in sputter gas. Further, if avery small amount of boron (B) is added into the amorphous silicon film,several tens ppm to several thousands ppm of boron (B) can be added intothe target in advance or diborane (B₂H₆) can be doped into the sputtergas.

A silicon oxide film that is applicable for the channel protection films119 through 122 can be manufactured by using silicon oxide (or quartz)as the target material and then sputtering Ar or mixed gas of Ar andoxygen (O₂). A silicon nitride film, a silicon oxide film, or a siliconoxide nitride film used for forming the protection insulating film 137,the interlayer insulating film 138, the passivation film 144 can bemanufactured in the same way as mentioned above.

If Al is used for the source wirings 139 through 141 and the drainwirings 142 and 143, then about 0.01 to 5 wt % elements such as Ti, Si,scandium (Sc), vanadium (V), or Cu is contained so that hillock can beeffectively prevented. Ti, Ta, Al, and the like used for the lightshielding film 171 and ITO, ZnO, SnO₂, and the like used for the pixelelectrode 146 can all be formed by the known sputtering method.

In this way, other than the second interlayer insulating film 145 andthe third interlayer insulating film 172 made of organic resin, any filmcan be formed by sputtering. Moreover, detailed experiment conditionscan be appropriately determined by a user.

Embodiment 6

Another example of the pixel TFT and the TFT of the drive circuit,particularly the P-channel TFT is indicated in this embodiment. First ofall, perform the processes of from FIG. 1A to FIG. 2A in the same way asexplained in Embodiment 1. The drawing of FIG. 12A corresponds to FIG.2A. It illustrates a state in which resist masks 1123 through 1125 andimpurity regions 1126 through 1130, doped with an impurity element thatgives n-type, are formed.

The forming of the p⁺ is then carried out as shown in FIG. 12B. A mask1131 is formed on a channel protection insulating film 1119 so as to bepositioned on the inside, and a region in which the N-channel TFT isformed is entirely covered by resist masks 1132 and 1133. Furthermore, achannel protection film 1119 b having a new shape is formed byperforming etching, that is, wet etching is carried out on the channelprotection film 1119 using fluorine-based solution so that the endportion of the film 1119 almost coincides with the end portion of themask 1131. Thereafter, high concentration impurity regions 1134 through1136 are formed by ion doping (ion implantation can be used) usingdiborane (B₂H₆). An impurity element is added into the impurity regions1134 through 1136 from the surface of the crystalline silicon film.

The range of boron concentration in this region is 1.5×10²⁰ to 3×10²¹cm⁻³, here it is 2×10²¹ cm⁻³. In this specification, the concentrationof the impurity element that gives p-type included in the impurityregions 1134 through 1136 formed here is expressed as “p⁺”. In this way,by providing the end portion of the high concentration impurity regionsin the P-channel TFT that, comes in contact with the channel formingregion more to the side of the channel forming region than to the endportion of the low concentration impurity regions 1113 and 1114 formedin the previous process, the junction condition in this portion can bemade into a good one.

As shown in FIGS. 1B to 2A, the impurity regions 1135 and 1136 are addedwith phosphorus (P) in the previous process, therefore a regioncontaining a mixture of boron (B) and phosphorus (P) is formed. However,in this process, by adding boron (B) at a concentration of 1.5 to 3times higher than that of the previous process, p-type conductivity canbe secured and no influences are inflicted upon the characteristics ofthe TFT. In this specification, this region is referred to as impurityregion “B”. Also, the impurity region 1134 at the side of the channelforming region is a region containing boron (B) only, and this region isreferred to as region “A” in this specification.

Respective impurity elements are selectively added into the crystallinesilicon film and then etching is carried out on this crystalline siliconfilm so that it is divided into island-like films. Then a protectioninsulating film 1137, which will later become a portion of the firstinterlayer insulating film, is formed. The protection insulating film1137 can be formed of a silicon nitride film, a silicon oxide film, asilicon oxide nitride film, or a lamination film of the combinationthereof and may be at a thickness of 100 to 400 nm.

Thereafter, the heat treatment process is carried out for the purpose ofactivating the impurity elements giving either an n-type or p-type thathave been added at respective concentrations. When activation is carriedout by furnace annealing, heat treatment is performed at 300 to 650° C.,preferably 500 to 550° C. in a nitrogenic atmosphere. In this process,heat treatment was performed at 525° C. for 4 hours. When laserannealing is applied, irradiation is conducted by using the excimerlaser as a light source, forming the laser light into a linear beamhaving a width of 100 to 500 ìm by an optical system and irradiating thelinear beam at the oscillation frequency of from 10 to 100 Hz; theoscillation pulse width of from 20 to 50 nsec (preferably 30 nsec), andthe energy density of from 100 to 500 mJ/cm². Another heat treatment isperformed at 300 to 450° C. for 1 to 12 hours in an atmospherecontaining 3 to 100% of hydrogen to hydrogenate the active layer. Thisprocess is to terminate the dangling bonds in the active layer bythermally excited hydrogen. As other hydrogenation means, plasmahydrogenation (using hydrogen excited by plasma) can be performed.

After completing the activation process, an interlayer insulating film1138 is formed at a thickness of 500 to 1500 nm on the protectioninsulating film 1137. A lamination film formed of the above insulatingfilm 1137 and the interlayer insulating film 1138 functions as a firstinterlayer insulating film. A contact hole that reaches the sourceregion or drain region of the respective TFT is next formed, and thensource wirings 1139 through 1141 and drain wirings 1142 and 1143 areformed. Though not shown, this electrode according to the presentembodiment is a laminated film of a three-layered structure consistingof a 100 nm Ti film, a 300 nm aluminum film containing Ti, and a 150 nmTi film which are formed by sputtering in successions.

The protection insulating film 1137 and the interlayer insulating film1138 can be formed of a silicon nitride film, a silicon oxide film or asilicon oxide nitride film, or the like. In any case, it is better thatthe internal stress of the film be made into the compression stress.

Next, using a silicon nitride film, a silicon oxide film, or a siliconoxide nitride film, a passivation film 1144 is formed at a thickness of50 to 500 nm (typically 100 to 300 nm). If hydrogenation process iscarried out in this state, desirable effects can be achieved withrespect to improving the characteristics of TFTs. For instance, it isbetter if heat treatment is performed at 300 to 450° C. in an atmospherecontaining 3 to 100% of hydrogen for 1 to 12 hours or by employing aplasma hydrogenation method in which similar effects can be obtained.Moreover, an opening may be formed in the passivation film 1144 at aposition where a contact hole for connecting a pixel electrode to thedrain wiring is to be formed.

Thereafter, a second interlayer insulating film 1145 formed of organicresin is formed at about 1 ìm of thickness in the same way as that ofEmbodiment 1. Then, a contact hole that reaches the drain wiring 1143 isformed in the second interlayer insulating film 1145 and the passivationfilm 1144, thus, a pixel electrode 1146 is provided. If a transmissiontype liquid crystal display device is to be manufactured, a transparentinsulating film is used to form the pixel electrode 1146. On the otherhand, if it is a reflector type liquid crystal display device that is tobe manufactured, a metallic film is used. Aimed here is a transmissiontype liquid crystal device, and therefore an indium tin oxide (ITO) filmis formed at a thickness of 100 nm by sputtering. A pixel electrode 1190is the electrode of a neighboring pixel.

From the above processes, the pixel TFT of a display portion and the TFTof the drive circuit in the periphery of the display portion are formedon the same substrate. In the drive circuit, an N-channel TFT 1168 and aP-channel TFT 1167 are formed, and a logic circuit structured with aCMOS circuit as the basic circuit can be formed. A pixel TFT 1169 is anN-channel TFT, and furthermore, a storage capacitor is formed from thecapacitor wiring 105, a semiconductor layer 1166, and an insulating filmformed therebetween, and is connected to this pixel TFT 1169 (FIG. 3).

A P-channel TFT 1167 of the drive circuit has a channel forming region1147, source regions 1148 and 1150 and drain regions 1149 and 1151;which are formed in high concentration impurity regions. The sourceregion 1150 and the drain region 1151 are formed in the impurity region“B”. The concentration of boron (B) in the regions is adjusted to have aconcentration 1.5 to 3 times higher than the concentration ofphosphorous (P). On the inside of the impurity region “B”, that is, thesource region 1148 and the drain region 1149 formed on the side of thechannel forming region 1147 is the impurity region “A”. This impurityregion “A” is a region containing only boron in the same concentrationas that of the impurity region “B”. The structure here is that theentire region “A” overlaps the gate electrode 1102 while on the otherhand a portfon of the region “B” overlaps the gate electrode 1102. Inthis way, by forming the high concentration impurity region in theP-channel TFT from the region “A” and the region “B” from and by formingthe region “B” far away from the channel forming region, the junction ofthe channel forming region and the high concentration impurity regioncan be a good one.

An N-channel TFT 1168 of the drive circuit has a channel forming region1152, a source region 1155 and a drain region 1156, and LDD regions 1153and 1154. The pixel TFT 1169 has channel forming regions 1157 and 1158,source regions or drain regions 1163 through 1165, and LDD regions 1159through 1162. The LDD regions in the N-channel TFT of the drive circuitare provided with the principal purpose of preventing the deteriorationof the on-current value due to hot carrier implantation by relaxing highelectric field in the vicinity of the drain. Thus, it is appropriate tomake the concentration of a suitable impurity element that gives n-typeat 5×10¹⁷ to 5×10¹⁸ cm⁻³. On the other hand, the principal purpose ofproviding the LDD regions in the pixel TFT is to decrease theoff-current value. The concentration of an impurity element in theseregions may be the same as those in the LDD regions in the N-channel TFTin the drive circuit, or may be ½ to 1/10 of that concentration. In FIG.13, although the pixel TFT 1169 is completed as a double-gate structure,it can also be a single-gate structure, or a multi-gate structureprovided with a plurality of gate electrodes without causing anyproblem.

In a TFT manufactured by the above process, the channel protectioninsulating film 1119 b and channel protection insulating films 1120through 1122 can be formed without receiving any damages from ion dopingor the like. Therefore, the characteristics of the TFT are stable. Forinstance, when a voltage of −1.7 MV is applied to the gate electrode andthen leaving it for an hour at 150° C. as a bias thermal stress (BTS)test, hardly any fluctuations can be observed in the threshold voltage,the field effect mobility, the sub-threshold constant, the on-currentvalue, etc. Furthermore, according to the present invention, theoperation performance and the reliability of a semiconductor device canbe improved by optimizing the structures of the TFTs that compose thepixel TFT circuit and the driver circuit in accordance with thespecifications of the respective circuits demand.

Also, regarding the structure of the storage capacitor shown in FIG. 13,it can be formed from the light shielding film, the dielectric filmformed on the surface of the light shielding film by anodic oxidation,and the pixel electrode according to embodiment 4 explained withreference to FIGS. 6A to 7B.

Embodiment 7

In this embodiment, processes of manufacturing an active matrix liquidcrystal display device from a substrate in which a pixel TFT and a drivecircuit are formed are described hereon. As shown in FIG. 8, anorientation film 601 is formed on a substrate in the state shown in FIG.3 manufactured according to embodiment 1. Normally, polyimide resin isoften used as an orientation film in a liquid crystal display device. Alight shielding film 603, a transparent conductive film 604, and anorientation film 605 are formed on an opposite substrate 602. Afterforming the orientation film, a rubbing operation is performed so thatthe crystal molecules are orientated at a fixed pre-tilt angle. Thenusing a well-known cell assembling process, the opposite substrate andthe other substrate on which the pixel TFT the drive circuit are formedare stuck together with sealing materials or a spacer (both not shown).Then after injecting a liquid crystal material 606 between the twosubstrates, the liquid crystal material is completely sealed by asealing agent (not shown). It is appropriate to use well-known liquidcrystal material as the liquid crystal material. The active matrixliquid crystal display device shown in FIG. 8 is completed in this way.

Next, a structure of the active matrix liquid crystal display devicewill be described with reference to the perspective view of FIG. 9 andto the top view of FIG. 10. It should be noted that the same referencenumerals as that of FIGS. 1A to 3 and FIG. 8 are used in FIGS. 9 and 10in order to correlate the latter with the sectional structural views ofthe former. Further, the sectional structure along the line A-A′indicated in FIG. 10 corresponds to the cross-sectional view of thepixel TFT 169 and the storage capacitor 170 shown in FIG. 3.

In the perspective view shown in FIG. 9, the structure of the activematrix liquid crystal display comprises a display region 701, a scanning(gate) line drive circuit 702, and a signal (source) line drive circuit703, which are formed on the glass substrate 101. The pixel TFT 169 isformed in the display region and the drive circuit formed in theperiphery of the display region is structured with a CMOS circuit as thebasic circuit. The scanning (gate) line drive circuit 702 and the signal(source) line drive circuit 703 are connected to the pixel TFT in thedisplay region 701 by the gate wiring 104 (denoted by the same referencenumeral as the gate electrode, for the wiring 104 is formed by extendingthe gate electrode and is connected thereto) and the source wiring 141,respectively. An FPC731 is connected to an external input/outputterminal 734.

FIG. 10 is a top view of almost an entire pixel of the display region701. The gate wiring 104 intersects with an active layer under a notshown gate insulating film via this gate insulating film. And also notshown, the active layer is formed of a source region, a drain region,and an LDD region formed of the n⁻ region. Further, reference numeral180 denotes a contact portion of the source wiring 141 and the sourceregion 163, 181 denotes a contact portion of the drain wiring 143 andthe drain region 165, and 182, a contact portion of the drain wiring 143and the pixel electrode 146. The storage capacitor 170 is formed of asemiconductor layer 166 that comes in contact with the drain region 165of the pixel TFT 169, the capacitor wiring 105, and a region which isformed therebetween and overlaps with the insulating film.

The active matrix liquid crystal display device is explained applyingthe structure in Embodiment 1, it is also possible to fabricate anactive matrix liquid crystal display device freely combined with any ofEmbodiments 1 to 6.

Embodiment 8

The substrate manufactured by carrying out the present invention andhaving a pixel TFT and a drive circuit which are formed on the samesubstrate may be used in various electro-optical display devices (activematrix liquid crystal display devices, active matrix EL display devices,and active matrix EC display devices). In other words, the presentinvention may be embodied in all kinds of electronic equipment having asdisplay medium those electro-optical display devices incorporatedtherein.

As such electronic equipment, there are enumerated: video cameras;digital cameras; projectors (rear projectors or front projectors); headmount displays (goggle type displays); navigation systems for vehicles;personal computers; portable telephones; and electronic books. Specificexamples thereof are shown in FIG. 11.

FIG. 11A shows a portable telephone that is composed of a main body9001, a sound output section 9002, a sound input section 9003, a displaydevice 9004, operation switches 9005, and an antenna 9006. The presentinvention can be applied to the sound output section 9002, the soundinput section 9003, and the active matrix display device 9004 providedwith a display region and a drive circuit that is formed in theperiphery thereof.

FIG. 11B shows a video camera that is composed of a main body 9101, adisplay device 9102, a sound input section 9103, operation switches9104, a battery 9105, and an image receiving section 9106. The presentinvention can be applied to the sound input section 9103, to the activematrix display device 9102 provided with a display region and a drivecircuit that is formed in the periphery thereof, and to the imagereceiving section 9106.

FIG. 11C shows a mobile computer that is composed of a main body 9201, acamera section 9202, an image receiving section 9203, operation switches9204, and a display device 9205. The present invention can be applied tothe image receiving section 9203, and to the active matrix displaydevice 9205 provided with a display region and a drive circuit that isformed in the periphery thereof.

FIG. 11D shows a goggle type display that is composed of a main body9301, display devices 9302, and arm sections 9303. The present inventioncan be applied to the active matrix display device 9302 provided with adisplay region and a drive circuit that is formed in the peripherythereof. Though not shown, the invention is also applicable to othersignal controlling circuit.

FIG. 11E shows a rear type projector that is composed of a main body9401, a light source 9402, a 9 display device 9403, polarizing beamsplitter 9404, reflectors 9405 and 9406, and a screen 9407. The presentinvention can be applied to the active matrix display device 9403provided with a display region and a drive circuit that is formed in theperiphery thereof.

FIG. 11F shows a portable electronic book that is composed of a mainbody 9501, display devices 9502, 9503, a memory medium 9504, anoperation switch 9505 and an antenna 9506. The book is used to displaydata stored in a mini-disk (MD) or a DVD, or a data received with theantenna. The display devices 9502, 9503 are direct-vision type activematrix display devices provided with a display region and a drivecircuit that is formed in the periphery thereof, to which the presentinvention may be applied.

Other than those, though not shown, the present invention may also beapplied to display sections of navigation systems for vehicles, imagesensors and personal computers. The present invention thus has so wideapplication range that it is applicable to electronic equipment in anyfield. Further, the electronic equipment of this embodiment can berealized using a structure formed by combining Embodiments 1 to 7. Nolimitation is put on how to combine these embodiments.

By implementing the present invention, it is possible to arrange TFTswith appropriate performances that meet the specifications demanded bythe functional circuits in the semiconductor device (specifically theelectro-optical device in the present invention) formed of a multiple offunctional circuits on the same substrate; and a substantial improvementcan be made in the operation characteristics and reliability.

More particularly, a bottom-gate TFT or an inverted stagger TFT providedwith the LDD regions, by forming as the LDD regions of the pixel TFT,Loff and Loy regions with n⁻ concentration, the off-current value can besubstantially decreased and contributions can be made to the low powerconsumption of the pixel TFT. Also, by forming, as the LDD regions inthe N-channel TFT in the drive circuit, Loff and Lov regions with n⁻concentration, the electric current drive performance can be enhanced aswell as preventing deterioration caused by hot carrier, and thedeterioration of the on-current value can be decreased.

Furthermore, the P-channel TFT of the drive circuit has the impurityregion “B” containing both an impurity element that gives p-type and animpurity element that gives n-type therein and has an impurity region“A” containing an impurity element that gives p-type therein. Theimpurity region “A” is formed between the impurity region “B” and theLDD region in the P-channel TFT in the drive circuit, securing thejunction between the channel forming region and the LDD region thatcomes in contact with the channel forming region, and between the LDDregion and either the source region or the drain region become.Therefore, the characteristics of the P-channel TFT can be wellretained.

Moreover, the operation performance and reliability of a semiconductordevice (specifically an electronic equipment in the present invention)having this type of electro-optical device as a display medium can beimproved.

1. A semiconductor device comprising: at least a first n-channel thinfilm transistor being formed in a display region over a substrate; atleast a second n-channel thin film transistor and at least a p-channelthin film transistor in a drive circuit each being formed in a peripheryof the display region over the substrate; and a capacitor formingelectrode formed adjacent to a portion of a crystalline semiconductorfilm to form a capacitor; the first n-channel thin film transistorincludes: gate electrodes formed over the substrate, a first insulatingfilm formed over the gate electrodes, a second insulating filmcomprising silicon oxide formed over the first insulating film, thecrystalline semiconductor film formed over the second insulating film,wherein the first n-channel thin film transistor has first and secondchannel regions, and source and drain regions, and wherein a channellength of the p-channel thin film transistor is shorter than that of thesecond n-channel thin film transistor.
 2. A device according to claim 1,wherein the crystalline semiconductor film of the second n-channel thinfilm transistor comprises a pair of LDD regions located between achannel region and source and drain regions respectively.
 3. A deviceaccording to claim 1, further comprising: an interlayer insulating filmformed over the crystalline semiconductor film of the first n-channelthin film transistor, a wiring formed over the interlayer insulatingfilm, the wiring connected to one of the source region or the drainregion, wherein the wiring overlaps one of the first channel region orsecond channel region.
 4. A device according to claim 1, wherein thegate electrodes comprise at least a material selected from the groupconsisting of tantalum, titanium, tungsten, molybdenum, and aluminum. 5.A device according to claim 1, wherein the semiconductor device is oneselected from the group consisting of a cellular phone, a video camera,a mobile computer, a goggle-type display, a projector, a mobile book, adigital camera, a car navigation device, and a personal computer.
 6. Adevice according to claim 1, wherein the first insulating film comprisessilicon nitride.
 7. A semiconductor device comprising: at least a firstn-channel thin film transistor being formed in a display region over asubstrate; and at least a second n-channel thin film transistor and atleast a p-channel thin film transistor in a drive circuit each beingformed in a periphery of the display region over the substrate; each ofthe second n-channel thin film transistor and the p-channel thin filmtransistor includes: gate electrodes formed over the substrate, a firstinsulating film formed over the gate electrodes, a second insulatingfilm comprising silicon oxide formed over the first insulating film, acrystalline semiconductor film formed over the second insulating film,wherein a channel length of the p-channel thin film transistor isshorter than that of the second n-channel thin film transistor, whereinthe first n-channel thin film transistor has at least first and secondchannel regions, and source and drain regions, wherein the crystallinesemiconductor film of the second n-channel thin film transistorcomprises a pair of LDD regions located between a channel region andsource and drain regions respectively.
 8. A device according to claim 7,further comprising: an interlayer insulating film formed over thecrystalline semiconductor film of the first n-channel thin filmtransistor, a wiring formed over the interlayer insulating film, thewiring connected to one of the source region or the drain region,wherein the wiring overlaps one of the first channel region or secondchannel region.
 9. A device according to claim 7, wherein at least aportion of the LDD region of the first n-channel thin film transistor isformed so as to overlap with the gate electrodes of the first n-channelthin film transistor, wherein at least a portion of the LDD region ofthe second n-channel thin film transistor is formed so as to overlapwith the gate electrode of the second n-channel thin film transistor.10. A device according to claim 7, wherein the semiconductor device isone selected from the group consisting of a cellular phone, a videocamera, a mobile computer, a goggle-type display, a projector, a mobilebook, a digital camera, a car navigation device, and a personalcomputer.